AU612053B2

AU612053B2 - Hydraulic steel mine-prop

Info

Publication number: AU612053B2
Application number: AU38424/89A
Authority: AU
Inventors: Martha-Catharina Heiliger
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-07-04
Filing date: 1989-07-01
Publication date: 1991-06-27
Anticipated expiration: 2009-07-01
Also published as: EP0349942A1; ES2036303T3; RU1838622C; BG51165A3; HUT52840A; ATE82616T1; US5051039A; TR23904A; NO901014L; HU893797D0; PL160886B1; WO1990000217A1; NO901014D0; DE58902744D1; HU207143B; UA18636A; GR3006458T3; JPH03500314A; EP0349942B1; DE8808519U1

Abstract

PCT No. PCT/DE89/00436 Sec. 371 Date Mar. 2, 1990 Sec. 102(e) Date Mar. 2, 1990 PCT Filed Jul. 1, 1989 PCT Pub. No. WO90/00217 PCT Pub. Date Jan. 11, 1990.Hydraulic steel mine prop having a bottom ram including an outer cylindrical tube (1) having a cylinder bottom (14) and an end collar (16), as well as a top ram guided coaxially slideably in the bottom ram by the end collar (16) and a guide ring (12). The top ram is a cylindrical tube (2) comprising a piston (9) sealed and guided relative to the inner wall of the outer cylindrical tube (1). A prop head (4), a setting and withdrawal valve (21), an inner extension stroke limiter, and a return spring (6) are also provided. Each of the outer and the inner cylindrical tubes is received at its facing ends by corresponding projections or facing end grooves of the end collar or piston at one end and at the prop head or cylinder bottom at the other end. Seals are provided at least at the piston, the prop head, and the cylinder bottom. An element is provided between the prop head and the piston for taking up tension forces between these two structural parts. A further tension element (7) arranged coaxially to the cylindrical tubes, is attached to the cylinder bottom. The element (7) extends as a holding rod through the piston and has a holding element (8) at its free end. A compression spring (6) is arranged coaxially to the tension element to act as a return spring.

Description

r i- 'JPI DATE 23/01/90 AOJP DATE 22/02/90 APPLN. ID 38424 89 PCT NtJMRFR PCT/flF89/0O3f

PCT

INTERNATIO1 INTERNATIONALE ZUSAMMENARBEIT AUP DEM GEBIET DES PATENTWESENS (PCT) (51) Internationale Patentklassifikation 5 (11) Internationale Veriffentlichungsnummer: WO 90/00217 E21D 15/44 Al (43) Internationales Veriffentlichungsdatum: 11. Januar 1990 (11.01.90) (21) Internationales Aktenzeichen: (22) Internationales Anmeldedatum: PCT/DE89/00436 1. Juli 1989 (01.07.89) Prioritftsdaten: G 88 08 519.8 U 4. Juli 1988 (04.07.88) Veriffentlicht Mit internationalem Recherchenbericht.

612053 (71)(72) Anmelder und Erfinder: HEILIGER, Martha-Catharina [DE/DE]; Hochkoppel 11, D-5166 Kreuzau-Untermaubach (DE).

(74)Anwalt: LIERMANN, Josef-Schregel-Str. 19, D-5160 Diiren (DE).

(81) Bestimmungsstaaten: AU, BG, HU, JP, KR, NO, SU, US.

(54)Title: HYDRAULIC STEEL MINE-PROP (54) Bezeichnung: HYDRAULISCHER STAHLGRUBENSTEMPEL (57) Abstract Hydraulic steel mine-prop having a lower prop comprising an external cylinder (1) with a cylinder base (14) and a collar ring as well as an upper prop arranged in the lower prop in such a manner that it can be coaxially moved by the collar ring (16) and by a guiding ring Said upper prop consists of a cylinder having a piston sealed against the internal wall of the external cylinder and a prop-head Said hydraulic steel mine-prop also comprises a fitting and drawing valve an internal extension limiting means and a return spring The external and internal cylinders are contained on their frontal extremities by corresponding fitting strips or frontal grooves on the collar ring or piston on the one hand, and on the prop-head or cylinder base on the other hand, and are sealed at least against the piston, prop-head and cylinder base. An element which absorbs t' e tensile forces between prop-head and piston is provided between the latter two parts. A further tension elemeat arranged coaxially relative to the cylinders, is mounted on the cylinder base. Said tension element extends as a stay bar through the piston and has, in the region of its free end, a holding element whereby a compression spring is arranged coaxial to the tension element and acts as a return spring, which is supported, on the one side, on the retaining element and, on the other side, on the tension-force absorbing element or on the piston or on a part which is connected to said element or to the piston, whereby the connection between fitting and drawing valve, on the one hand, and pressure chamber, on the other hand, is effected over the prop-head or the cylinder base.

HYDRAULIC STEEL MINE PROP The invention relates to a hydraulic steel mine prop including a bottom ram basically consisting of an outer cylindrical tube with, on the one hand, a cylindrical floor and, on the other hand, an end collar, as well as a top ram guided on the one e'-g.

hand coaxially slideably in the bottom ram by means of the end collar via at least a guide ring. The top ram basically consists of a cylindrical tube, which, on the one hand, has 0* O a piston sealed off and guided relative to the inner wall of the outer cylindrical tube and, on the other hdnd, a prop head, and further includes a setting and withdrawal valve, an inner stroke limitation and a return spring.

e C S" A mine prop of the above described type has, for example, become known from the DE-OS 3,541,871. Such mine props have been completely successful regarding their functionality.

Such steel mine props are known in numerous structural variations. Due to their great weight, attempts have already been made to produce such mine props of light metal. However, ,uch light metal mine props are not usable wherever the danger of firedamp exists, because even slight impacts on Che light metal tubes can produce sparks which then can cause a gas explosion. Moreover, such light metal mine props are also about twice as expensive as corresponding steel mine props.

1 YIIIIUI rsl pl 1 0 0 0: 0 0 4' In steel mine props of the known type, an outer cylindrical tube is welded to a cylindrical floor or a prop foot. Because this outer cylindrical tube serves as a running bushing for the inner piston of the inner cylindrical tube, normally it is machined precisely by drilling and subsequent'grinding or honing. It is furthermore surface treated, for example, with cadmium or ziiic. A groove is turned-in in the head region of the outer prop tube for holding the end collar with the handle which is arranged in that region, whereby the holding is achieved by means of a groove wire, which is laid into the corresponding groove. The end collar additionally has the purpose to function as an extension stroke stop for the inner cylindrical tube. In order to determine the extension Stroke length, a stop bushing is inserted between the inner cylindrical tube and the outer cylindrical tube, and is taken along by the piston of the inner cylindrical tube during the extension stroke movement. Corresponding to the length of this stop bushing, the stop bushing will abut against the stop surface of the end collar with the inner cylindrical tube driven out more or less far, whereby a further extension of the inner cylindrical tube becomes impossible. The end collar in turn represents a second guide for the inner cylindrical tube. However, the end collar must now take up the full axial force created by the prop and transfer this force via the groove wire onto the outer cylindrical tube. Due to the fact that the outer cylindrical tube is welded to a cylindricalbottom, easily weldable material must be used for this tube and therefore high strength steel alloys cannot be used. Due to the arising load, pressures of about 2i Ll 1i )i -L 2 I ~r~lru~ 400 bar arise in the outer cylindrical tube, this cylindrical tube has a correspondingly large wall thickness and therewith a corresponding weight. Here it must be remembered that transportation and erection of such mine props in practice is done exclusively manually.

The valve housing for the setting and withdrawal valve is welded on at a suitable location. This welding work and the welding work by means of which the outer prop tube is welded to the bottom, produces deformations, which, on the one hand, negatively influence the tight sealing of the valve insert and, on the other hand, damage the mentioned surface 0* treatment of the tubes.

Moreover, it is to be considered that turning-in the groove oooeo for the groove wire of the end collar weakens the outer prop tube so that a corresponding increase in wall thickness is S* necessary.

The internal stop sleeve can easily become encrusted and thereby' prevent pushing the prop tubes together. Moreover, because this sleeve moves along with the extension and withdrawal motion of the inner prop, damage to the surface protection of the inner surface of the outer prop is unavoidable as well.

From the described construction features it can be seen that the known construction of steel mine props sire very heavy, and it can easily be recognized that repairing such props is not K4tIr -3 0477v/MS i

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0 possible without qualified personnel and without technical equipment of high quality machine tools. In any case, independently thereof, when making repairs at least the surface protection of the prop tubes will be damaged. Moreover, because different lengths of steel mine props are required due to the different structural heights, a suitable number of the required different lengths must always be kept in stock. It is not possible to produce such mine props according to requirements in an above-mentioned workshop on site. According to the DE-OS 3,541,871, it is already seen as a great advance that a prop assortment of "only" eight different lengths must be produced for the different structural heights arising in practice.

In one broad form the present invention is a hydraulic steel mine prop having a bottom ram comprising an outer cylindrical tube having a cylinder bottom at one end and an end collar at the other end, a top ram guided coaxially and slideably displaceable in said bottom ram by means of the end collar through at least one guide ring on said end collar, said top ram comprising an inner cylindrical tube having at one end a piston sealed off and guided relative to the inner wall of the outer cylindrical tube and, at the other end, a prop head, said prop further having a setting and withdrawal valve, an inner stroke limiting means and a return springr, wherein the outer and the inner cylindrical tubes are received at the respective facing ends by corresponding projections, or facing end grooves of said end collar, or the piston, at one end, and are received by a prop head or a cylinder bottom at the other U1 I- 7 A K1 -4 0477v/MS end, said ends being sealed off at least at the piston, at the prop head and at the cylinder bottom, and an element is provided between the prop head and the piston for taking up tension forces between these two structural components, that a further tension element arranged coaxially to the cylindrical tubes, is attached to the cylinder bottom, said further tension element extending as a holding rod through the piston and B comprising a holding member in the regio- of the free end, wherein a compression spring is arranged coaxially to the e tension element to act as a return spring which is secured at one end to the holding member and at the other end to the element, which takes up tension forces, or at the piston or a structural part connected to the element or the piston, and wherein the connection between the setting and withdrawal valve and the pressure chamber is achieved through the prop head or through the cylinder bottom.

.In a hydraulic steel mine prop of the present invention, the outer and the inner cylindrical tube each respectively is received at its face side ends by corresponding projections of face side grooves of the end collar or the piston, on the one r e hand, and the prop head or the cylindrical bottom, on the i; 4a- 6'I L i Oj other hand, and are sealed off at least at the piston, at the prop head and at the cylindrical bottom. Furthermore, an element is provided between the prop head and the piston for taking up tension forces between these two structural parts. Also, a further tension element arranged coaxially to the cylindrical tubes, is attached at the cylindrical bottom and extends as a holding rod through the piston, and has a holding element in the region of the free end, whereby a compression spring is arranged coaxially to the tension element or to act as a return spring, which is supported, on the one hand, at the holding element and, on the other hand, at the element which takes up the tension forces, or at the piston, *5 S* or at a structural component connected to the element or the piston, and wherein the connection between the setting and withdrawal valve, on the one hand, and the pressure chamber, Set...

S on the other hand, takes place through the prop heac' or the cylindrical bottom. The construction suggested according to the invention S. does not require any welding work. Hence, it is no longer necessary to select a material which can be easily welded, rather, in contrast, a high strength material may be selected for example for the cylindrical tubes. Thereby the wall thicknesses of the cylindrical tubes can be kept thinner, whereby the prop becomes lighter. The prop tubes, at their respective face side ends, are simply set onto corresponding projections or set into corresponding grooves. There, they are no longer welded, but are merely sealed off. This sealing can be achieved for example, by means of an inner O-ring and, if necessary, additionally by an outer O-ring. However, it is preferably 1' 5

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achieved by means of the conventionally known and highly effective liquid seals, which cure at room temperature and remain absolutely tightly sealed even at the highest pressures. This simple application of the cylindrical tubes with simple sealingsis possible because appreciable axial tensile loads need no longer be tLiken up by the cylindrical tubes in the prop according o to the invention. Thereby it is also possible to supply the ,0 prop in its individual parts without the cylindrical tube and to have in stock or to deliver tubes as yard goods, which tubes have been appropriately pre-machined and surface-treated if necessary. If a steel mine prop is to be produced for a particular structural extension height, then it is simply necessary to cut off ac appropriate lengths, for instance Que*We by nswi iq, the cylindrical tubes which have been stocked as S yard goods, to debur the saw cut ends of the tubes, to simply join lhe tubes with the allocated face side components, and to snal the tubes to the other components by means of the liquid seal, for example. No welding work is necessary, and the distortion of the tube, caused by welding, is avoided.

Also, damage to the treated surface is avoided. The damages caused in the cutting region by cutting off the tube, disappear in the seal and are thereby harmless.

6 T i M I II Tho invention will now be described in greater detail with reference to various example embodiments depicted in the drawings.

There is shown in: Fig. 1 a longitudinal section through a steel mine prop with a head connection of the setting valve; Fig. 2 a longitudinal section through a steel mine prop with a bottom connection of the setting valve and arrangement of the setting valve in the hand grip arranged on the outer cylindrical tube; Fig. 3 a longitudinal section as in Fig. 1, however with a high pressure relief valve at the piston; 9.

o Fig. 4 a longitudinal section as in Fig. 2, however with an excess pressure relief valve at the piston; i Fig. 5 a portion of a longitudinal section through a steel mine prop with a safety valve at the piston for limiting the extension stroke.

A steel mine prop according to Fig. 1 is essentially composed of an outer cylindrical tube 1, which is inserted at its lower face end into a corresponding face end groove of a cylindrical bottom 14' and is sealed there by a liquid seal 5. If necessary, 1 7 I I- ~Er transversely directed holding screws 23 can be provided as a simple mechanical lock. However, these cannot and should not transfer any appreciable mechanical loads. The cylindrical bottom 14' is inserted in a conventional manner in a so-called prop foot 25, which is attached to the cylindrical bottom 14', for example, by tension sleeves, of which only the bores 46 are illustrated.

An end collar 16, which may also be split, is put onto the other face end of the outer cylindrical tube 1, and centered by a simple centering projection. This end collar 16 comprises an inner guide ring 12 for an inner cylindrical tube 2 and a dirt scraper 17 for cooperating with the inner cylindrical tube 2.

An inner cylindrical tube 2 is guided longitudinally slideably, displaceably in the outer cylindrical tube 1 by the end collar 16 with its guide ring 12 arranged on the end collar 16. In the interior of the outer cylindrical tube 1, the inner cylindrical S. tube 2 comprises a piston 9 at the tube's facing end. This piston 9 comprises a receiving projection, which is not described in further detail, by means of which it can be pushed into the interior of the tube 2. Herewith the face end of the cylindrical tube 2 comes to rest against the end of the mentioned projection of the piston 9. This connection region of the inner cylindrical tube 2 with the piston 9 can in turn simply be sealed, preferably by means of a'liquid seal 5. The piston 9 is guided in the outer cylindrical tube 1 by means of a guide ring 12' and is sealed by means of a piston seal ring 8 -M M-- T'II outer facing end of the inner cylindrical tube 2 is inlsrted into a facing end annular groove of a valve housing 24, which groove is not described in further detail, and is sealed there in turn, preferably by means of a liquid seal 5. A setting and withdrawal valve 21 which is known as such, is located in this valve housing 24, in a manner known as such. The valve housing 24 is also formed on its upper side in a known manner such that there it can receive a prop head 4, which can be joined to the valve housing 24 in a conventional manner and which can be r supported by the valve housing 24, so that the support force can be transmitted via the prop head 4 and the valve housing 24 onto the inner cylindrical tube 2.

On the inner side of the valve housing 24, a bore which is not described in further detail, is provided and extends coaxially with the longitudinal axis of the steel mine prop. The bore is connected to the bore for the setting valve 21, and is equipped with a threading at its end pointing toward the interior of the cylinder.

A tube 3 is screwed into this threading, and is sealed in this thread region, in a manner not illustrated in detail, such that a pressure, which arises in the interior of the tube 3, cannot be communicated to its outside.

The other facing end of the tube 3 passes through a corresponding coaxial bore of the piston 9, which bore is not described in further detail. There the tube 3 is connected by means of a threaded nut 13, which can be embodied as a groove nut or circular nut.

In this context, the threaded nut 13 is supported by its inner flat surface against the corresponding counter surface of a 9 r I recess of the piston 9, and is also sealed in this region, so that a pressure arising in the pressure chamber 26 cannot be communicated in this region to the outside of the tube 3.

At the end connected to the threaded nut 13, the inner side of the tube 3 comprises a stop r.ng 11, against which a spiral compression spring 6 is supported with its facing end. This spiral compression spring extends into the interior of the tube 3, so that this tube 3 can also be referred to as a spring guide tube.

~However, as can be seen from the arrangement, the tube 3 joins .3F.

the valve housing 24 and therewith the prop head 4 to the piston 9, so that the tension forces created between these parts, are taken *up by the tube 3. However, the tube 3 does not take up compression 3. 4 S. forces. On the contrary, these are taken up by the cylindrical tube 2.

S The spiral compression spring 6 is supported at its second end 33.3 against a support element 8 which is arranged at an inner free end of a tension element 7 embodied as a rod. The second end of the tension element 7 passes through a corresponding bore in the cylindrical bottom 14', right through this cylindrical bottom, and is held in this position against being pulled out, by means of a retaining ring 47. A seal 48, arranged on the inner side, assures that at this location the pressure in the pressure chamber 26 cannot be communicated to the outside.

Due to the described arrangement of the spiral compression spring, it has the tendency to displace the piston 9 in the direction toward the cylindrical bottom 14' and thereby to retract the cylindrical tube 2. This is possible in a corresponding and known control -0 10 _m w

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position of the setting and withdrawal valve 21, namely when it is in the withdrawal position. The liquid present in the pressure chamber 26 is then displaced by the piston 9 due to the spring force of the spiral compression spring 6 and herewith it is pressed through the inner chamber of the tube 3, which still has sufficient space for this, and to the valve 21 and from there to the outside.

In opposite direction, that is, when the prop is to be extended for supporting the hanging roof of a seam or mine, the valve 21 is moved into the setting position so that the pressure medii"n generally plain water- can flow fron, the valve 21 into the interior of the tube 3 and from there into the pressure chamber 26. Hereby, the piston 9 and therewith the cylindrical tube 2 with its outer accessory structures are extended until the prop head 4 makes S* contact. If however, the prop has been embodied too short for any reason, then the compression spring 6 merely assumes a blocking function, whereby a further extension movement is prevented. Tensile loads J do not arise on the outer cylindrical tube 1 or on the end col- lar 16. A stop bushing is not required between the inner cylindrical tube 2 and the outer cylindrical tube 1. Corresponding surface damage that could be caused by such a bushing is avoided.

A handle 18, arranged on the outer surface 27 of the outer cylindrical tube 1, is embodied in split form in a manner known as such, but not illustrated in detail, and therefore the handle 18 can be clamped on the mentioned outer surface 27 or be displaced on it.

4 I 0 11 The embodiment according to Fig. 2 is almost identical in its internal construction to the embodiment according fo Fig. i.

Therefore, reference can be made to the above description of Fig. i. In the embodiment according to Fig. 2, the prop head 4 is merely integrally formed without the valve housing 24 described for Fig. i. In place thez-eof, according to the embodiment according to Fig. 2, the valve housing for the valve 21 is formed by a part 18' of the handle arranged on the outer surface 27 of the outer cylindrical tube i. However, this is also known as such. In the embodiment according to Fig. 2 the valve 21 is then joined to a connection piece 20 by means of a high pressure hosf 19 joined pressure tightly to the first ge part 18', which connection piece 20 is formed as an outer cam on the cylindrical floor 14. A bore 22 passes through this connection piece 20 and the adjoining part of the cylindrical 0 floor 14, into the interior of the pressure chamber 26, and passes below the annular groove, not described in detail, for receiving the outer cylindrical tube 1 so thu: the associated sealing region of the seal 5 is not touched. The mode of oper- @6 ation of the prop and the remaining construction is as already described with reference to Fig. 1. This arrangement has the advantage that the setting and withdrawal valve is always easily acce:sible even for large extension stroke lengths of the prop, and that, during the setting or withdrawal of the prop, i.ts height position is not changed.

Fig. 3 in turn shows a prop, which is identical in its construction in all essential characteristics to the prop according to Fig. i. Here, also reference can be made in this regard, 12 1 to the description of the prop of Fig. i. In the embodiment according to Fig. 3, however, the piston 9' comprises an excess pressure relief valve 15, which often is described as a working valve, and which iscoinnected at its inlet via a bore 30 to the pressure chamber 26, and at its outlet via a bore 31 to the intermediate chamber 28 between the outer cylindrical tube 1 and the inner cylindrical tube 2. Hereby, the mouth of the bore 31 lies above the piston seal ring 10 so that an unhindered entry to the mentioned intermediate chamber 28 is possible.

Simultaneously, the end collar 16 comprises at least one relief bore 29, which, on the one hand, terminates into the intermediate chamber 28 and, on the other hand, leads freely into the ambient air.

In case of overloading of the prop, the described excess pressure relief valve 15 at the piston 9' typically has the function of allowing a retraction of the inner cylindricdl tube 2 by an extent suitable to decrease the overload, which is achievable *n that the pressure of the pressure medium is decreased by appropriately bleeding the pressure medium from the pressure chamber 26 by means of the excess pressure relief valve The special arrangement and connection according to Fig. 3 now makes it possible to bleed off the excess pressure from the pressure chamber 26 through the bore 30 and through the excess pressure relief valve 15 and the outlet bore 31 into the intermediate chamber 28, and thereby to flush the water, which is typically used as the pressure medium, into this intermediate chamber 28, 13

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*T 5 and thereby simultaneously to wash this intermediate chamber free of dirt particles. The water exiting from the bore 31 then can leave the intermediate chamber 28 through the relief bore 29. Hereby, this cleaning process not only can occur upon overloading of the prop, but also can be intentionally caused to occur by running the pressure medium to excess pressure. In this manner, an active cleaning of the intermediate chamber 28 is mdcde possible for the first time.

Fig. 4 in turn shows a prop with the construction according to Fig. 2. However, in the embodiment according to Fig. 4, just as in the embodiment according to Fig. 3, the over-pressure relief valve 15 is provided at the piston 9' in the same arrangement and function as described with reference to Fig. 3.

However, the construction of the mine prop according to Fig. deviates in essential points from the previously described constructions. However, this relates only to the inner parts.

The outer cylindrical tube 1 and the inner cylindrical tube 2 comprise, at their respective facing ends, the same arrangements as have already been described with reference to Figs. 1 to 4.

In this context, in the region of the prop head 4, the tube 3 serving as a spring guide tube is attached to this prop head 4 or to a valve housing 24 in a similar manner as has already been described with reference to Figs. 1 to 4. In the example embodiment according to Fig. 5, however, the inner piston 37, connected to the inner cylindrical tube 2, is equipped with a safety valve 32. For this purpose, in the example embodiment according to Fig. 5, the piston 37 is divided transversely into 14

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two parts. The one part is embodied as a tube end plate 39 and is connected, similarly as the pistons 9 and by a seal to the inner cylindrical tube 2 on its facing end. This tube end plate 39 comprises a concentric bore with a threading, into which the tube 3 is screwed by means of a corresponding threading which is not designated in detail, and is sealed off there.

A stop element 40, actually serving as the piston, is screwed by means of screws 49 onto this tube end plate 39 on the facing end pointing toward the pressure chamber 26. These screws 49 are, of course, also sealed so that no pressure from the pressure chamber 26 can pass to the outside of the tube 3 and thereby S: into the inner chamber 38. While, in principle, this would not be damaging, it would, however, mean that pressure medium, generally water, is present in this chamber 38, whereby the oo total weight would be unnecessarily increased.

The stop element 40 comprises a central bore 45, which is someooooo what smaller in its diameter than the inner diameter of the tube 3, so that the spiral compression spring, in turn arranged in the tube 3, can be supported on its facing end in the region of the central bore 45 by the stop element The stop element 40 comprises a recess 41 with a bottom 42.

The safety valve 32 is fitted in a bore in the bottom 42, which bore is not referenced in detail, deeply enough that it does not project above the upper edge 43 of the recess 41.

Hereby, it is ensured that when the bottom of the piston 37 abuts against the cylindrical bottom 14', the corresponding load A/ T need not be taken up by the safety valve 32.

The safety valve 32 is joined by means of a bore 33 to the intermediate chamber 28. For this, the bore 33 passes above a guide ring 12 and a piston sealing ring 10 of the stop element 40 into the intermediate chamber 28, so that there the pressure fluid can emerge unhindered. The inlet side of the safety valve 32 joined to the pressure chamber 26 is not shown in detail and is provided at the valve itself.

For its operation, the safety valve 32 comprises a cam 34, which has a running wheel, not referenced in detail, which contacts the outer surface of a tension element 7' embodied as a rod or tube, whereby in this contact the safety valve 32 is egs.

closed. The tension element 7' in turn can ess' "ially be embodied like the tension element 7 according to Figs. 1 to 4. eee However, while in the embodiments according to Figs. 1 to 4, the spiral compression spring 6 was driven into a blocking state in the fully extended state of the prop, and thereby tensionloaded the tension element 7 with the entire prop support force, such a load no longer occurs in the tension element 7' and the spiral compression spring 6 in the embodiment according to eee• Fig. 5. Namely, the tension element 7' comprises an annular groove 35, which is provided axially in such a position that when the prop has been extended so far, that the spiral com-

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pression spring is just before the blocking position, the cam 34 drops into the annular groove 35 and thereby opens the safety valve 32. The pressure chamber 26 is hereby depressurized and the pressure medium is blown to the outside through the bore 33 into the intermediate chamber 28 and from there, for example, through relief bores 29 in the end collar 16. Therewith, a further i k- 6 16-

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0, 9@ 9 0 6O 04 55 0'4 -j' extension of the cylinder is impossible and thus the tension element 7' only has to take up the tension load resulting from the relatively small spring force of the spiral compression spring 6. Therefore, it is also possible to construct the tension element 7' as a tube, which is fitted at its end facing the cylindrical bottom 14' into a corresponding recess of the cylindrical bottom 14' and is sealed there. In this region it can comprise an inner thread which is not referenced in further detail. A threaded stopper 44 fitted from the outside through the cylindrical bottom 14', is inserted into this inner thread, whereby the stopper 44 axially holds the tension element 7' If it is desired, the tension element embodied as a tube, can also be open at its free facing end and comprise transverse bores 36, so as to avoid pressure being exerted by the pressure medium of the pressure chamber 26 onto the tension element 7' The embodiment according to Fig. 6 presents a variation in which the return spring is embodied as a tension spring in contrast to the example embodiments according to Figs. 1 to 5. This example embodimnent corresponds in its essential construction to the construction of the prop described with reference to Fig. 5. However, in the example embodiment according to Fig. 6, a tube 51 is used in place of the tension element 7' according to Fig. 5, which tube 51, just as the tension element 7' according to Fig. 5, extends through the piston 37 into the tube 3. The remaining construction of the arrangement according to Fig. 6 is just like the construction of the arrangement according to Fig. 5 except for the spring. However, in Fig. 6, a spiral 17 tension spring 50 is employed as a return spring, which extends in the interior cf the tube 3 on the one hand and tube 51 on the other hand, and which is attached at one end in a suitable manner, known as such,to the prop head 4 or to the respective valve housing 24, and at its other end to the threaded stopper 44. By means of this arrangement the spring, being under tension load, tends to contract and therewith tends to move the prop head 4 and the cylindrical bottom 14' closer together, whereby in the pressureless state of the prop it can be moved into position in a desired manner.

In the arrangement according to Fig. 6, the tube 51 serves simultaneously as a control rod for the safety valve 32. Namely, if the prop is extended out to its allowable limit position, then therewith the cam 34 of the safety valve 32 reaches the S° end 52 of the tube 51 so that the cam can extend unhindered and thereby open the safety valve 32 in the already described manner. In spite of maintaining this function, it is, of course, "also possible to make the tube 51 longer if care is taken *t that a recess or a groove or a slot is provided at the position 52.

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Claims

1. A hydraulic steel mine prop having a bottom ram comprising an outer cylindrical tube having a cylinder bottom at one end and an end collar at the other end, a top ram guided coaxially and slideably displaceable in said bottom ram by means of the end collar through at least one guide ring on said end collar, said top ram comprising an inner cylindrical tube having at one end a piston sealed off and guided relative to the inner wall of the outer cylindrical tube and, at the other end, a prop head, said prop further having a setting and withdrawal valve, an inner stroke limiting means and a return spring, wherein the outer and the inner cylindrical tubes are *l received at the respective facing ends by corresponding projections, or facing end grooves of said end collar, or the piston, at one end, and are received by a prop head or a cylinder bottom at the other en, said ends being sealed off at least at the piston, at the prop head and at the cylinder bottom, and an element is provided between the prop head and the piston for taking up tension forces between these two structural components, that further tension element arranged coaxially to the cylindrical tubes, is attached to the cylinder bottom, said further tension element extending as a holding rod .through the piston and comprising a holding member in the region of the free end, wherein a compression spring is arranged coaxially to the tension element to act as a return spring which is secured at one end to the holding member and at the other end to the element, which takes up tension forces, or at the piston or a structural part connected to the element or S- 19 Lz~-A ir 2 04r77v/MS the piston, and wherein the connection between the setting and withdrawal valve and the pressure chamber is achieved through the prop head or through the cylinder bottom.

2. A hydraulic steel mine prop as claimed in claim i, wherein a liquid seal is used as a seal, which solidifies and seals at room temperature and again becomes liquid at suitably high temperatures.

3. A hydraulic steel mine prop as claimed in claim 1 or 2, wherein the tension element is constructed as a tube one end of which is attached to the prop head and to the piston at the other end. oooo S: 4. A hydraulic steel mine prop as claimed in claim 3, wherein the tube is screwed directly to the prop head and the other end extends at least partially through the piston and is connected at this end with a threaded nut, which bears axially against the piston. A hydraulic steel mine prop as claimed in anyone of the preceding claims wherein the inner chamber of the inner cylindrical tube of the top ram is sealed pressure tightly relative to the pressure chamber of the steel mine prop.

6. A hydraulic steel mine prop as claimed in claim wherein the seal is achieved at one end by means of the connection of the piston with the inner cylindrical tube of the top ram and at the other end by means of seals in the region of the attachment of the tube to the respective structural elements.

7. A hydraulic steel mine prop as claimed in anyone of the preceding claims wherein the piston facing end of the tube or 0477v/MS of the pistons or of a structural part connected to the piston comprises an inner stop element concentric to and surrounding the tension element, whereby the compression spring bears against the stop element.

8. A hydraulic steel mine prop as claimed in anyone of the preceding claims wherein the compression spring is constructed as a spiral compression spring.

9. A hydraulic steel mine prop as claimed in claim 8, wherein the cross-section of the spring wire of the spiral compression spring is rectangular or square.

10. A hydraulic steel mine prop as claimed in anyone of the *o preceding claims wherein the inner diameter of the tube is only f.e: slightly larger than the outer diameter of the spiral compression spring driven to its blocking state. 6 11. A hydraulic steel mine prop as claimed in anyone of the preceding claims wherein the tension element is releasably attached to the cylinder bottom. S 12. A hydraulic steel mine prop as claimed in anyone of the SO preceding claims wherein the prop head is constructed in two parts, whereby an upper part forms the actual prop head, while a lower part is formed as a valve housing for a setting and withdrawal valve, which is inserted into the valve housing in a o: known manner.

13. A hydraulic steel mine prop as claimed in claim 12, wherein the inlet and the outlet of the valve are connected directly or through the valve housing, to the inner chamber of the tube and thus to the pressure chamber.

14. A hydraulic steel mine prop as claimed in anyone of the 21 I\ f A A 0477v/MS claims 1 to 10, with a divided handle, which is held tightly clampably and slideably displaceably on the outer surface of the outer cylindrical tube of the bottom ram, wherein a part of the handle is constructed as a valve housing for a setting and withdrawal valve, which is connected to the pressure chamber through a flexible high pressure hose and a further leading bore in the cylinder bottom and a connection piece arranged thereon. A hydraulic steel mine prop as claimed in anyone of the preceding claims wherein a relief bore is provided in the end collar connecting the ambient air with the intermediate chamber.

16. A hydraulic steel mine prop as claimed in claim wherein an excess pressure relief valve is arranged at the piston, and wherein the inlet side of the valve is connected to the pressure chamber and the outlet side of the valve is connected to the intermediate chamber.

17. A hydraulic steel mine prop as claimed in claim 16, wherein the excess pressure relief valve is arranged on the side of the piston away from the pressure chamber.

18. A hydraulic steel mine prop as claimed in claim 17, wherein the inlet side and the outlet side of the excess pressure relief valve are connected through bores to the pressure chamber and the intermediate chamber respectively, whereby the bore for connecting the outlet side to the intermediate chamber terminates directly above a piston sealing ring of the piston.

19. A hydraulic steel mine prop having a bottom ram comprising an outer cylindrical tube having a cylinder bottom 22 4 0477v/MS at one end and an end collar at the other end, a top ram guided coaxially and slideably displaceable in said bottom ram by means of the end collar through at least one guide ring on said end collar, said top ram comprising an inner cylindrical tube having at one end a piston sealed off and guided relative to the inner wall of the outer cylindrical tube and, at the other end, a prop head, said prop further having a setting and withdrawal valve, an inner stroke limiting means and a return spring, wherein the outer and the inner cylindrical tubes each is respectively received at one facing end by corresponding projections or facing end grooves of the end collar or piston, and at the other end by the prop head or the cylinder bottom, o. respectively, and are sealed off at least at the piston, at the prop head and at the cylinder bottom and an element is provided between the prop head and the piston for taking up tension forces between these structural parts, and the piston comprises a safety valve which, in a predetermined end position of the piston, connects the pressure chamber with the external surroundings through a bore and through the intermediate chamber and relief bores, and a spiral tension spring acting as a return spring is arranged under tension between the prop head and the cylinder bottom, said return spring being surrounded by *SSSSS 0* the element for taking up tension forces between the prop head and the piston and by a tube, which is attached to the cylinder bottom and which, at least in the retracted state of the prop, extends telescopically and surrounding the spiral tension spring, into the element constructed as a tube for operating the safety valve. -23 z 'Ir o^ 0477v/MS A hydraulic steel mirne prop as claimed in claim 19, wherein the safety valve comprises a cam for its operation, said cam contacting the surface of the tension element or of the tube, and which is transferred into a different switching state by means of a surface contour change in the position corresponding to the predetermined end position.

21. A hydraulic steel mine prop as claimed in claim wherein the surface contour change is embodied as an annular groove, or depression, or cut-in, or slot.

22. A hydraulic steel mine prop as claimed in claim wherein the surface contour change is embodied as the end of the tube.

23. A hydraulic steel mine prop as claimed in anyone of claims 19 to 22, wherein the piston comprises a recess on its side facing toward the pressure chamber, said safety valve being inserted in the bottom of said recess deep enough, so that the valve does not project above the upper edge towa'1s 5S5S55 the pressure chamber, said valve having an outlet connected to the bore. I I 24. A hydraulic steel mine prop as claimed in anyone of the claims 1 to 18 or 23, wherein the tension element is hollow at least over a part of its length, and is attached by means of a S threaded stopper to the cylinder bottom. A hydraulic steel mine prop as claimed in anyone of the claims 19 t_ 24, wherein the piston is divided transversely and comprises a tube end plate and a stop element connected axially in a direction toward the pressure chamber. 24 04,77v/MS

26. A hydraulic steel mine prop as claimed in claim wherein the stop element comprises the safety valve and the bore, at least one guide ring, and at least one sealing ring, and a central bore, whereby the inner wall of the bore is spaced away from the outer surface of the tension element or of the tube, so that a gap exists for the pressure medium to pass through.

27. A hydraulic steel mine prop as herein described and with reference to the accompanying drawings. EATED this 8th day of March, 1991. MARTHA CATHARINA HEILIGER By Her Patent Attorneys ARTHUR S. CAVE CO. 0e**: 0** 0 -0 C N 0' i 1 'A